It is known (U.S. Pat. No. 4,540,595) that one may mark documents such as bank checks by the use of inks that fluoresce in the near infrared region, i.e., generally between 650 and 800 nm, for automatic identification. Fluorescent phenoxazine dyes of the formula ##STR1## wherein R.sub.1 and R are alkyl and X.sup.- is an anion are shown to be effective near-infrared fluorescing compounds for this purpose. Attempts to use these compounds to impart fluorescence in the near infrared by adding them to water dissipatable polymers have failed because of poor thermal stability.
It has been proposed (G. Patonay, Analytical Chemistry, Vol. 63, No. 6, 1991, pp 321-327) to use near infrared fluorescent compounds for fluorogenic labels for biomolecules; however, the disclosed fluorescent compounds have poor thermal stability and are not suitable for adding to water-dissipatable polymers during preparation.
This present invention, as described below, relates to water-dissipatable (i.e., dispersible) polymeric compositions which are useful in the formulation of near infrared fluorescent inks, paints and film forming compositions. The polymeric compositions are unique in that the near infrared fluorophores (NIRF's) are copolymerized therein and thus are not extractable, exudable, sublimable or leachable from the polymeric composition. Also, since the NIRF is bound to polymer chain by covalent bonds or incorporated into the backbone of the polymer by covalent bonds, toxicological concerns are minimized because of low potential for exposure to humans. The inks, paints and film forming compositions prepared from the polymeric compositions of this invention are especially useful in "marking" or "tagging" various items, e.g. security documents, bank checks and other printed or coated materials where subsequent detection or identification is desired.